Touch screen sensors can detect the location of an object (e.g. a finger or a stylus) applied to the surface of a touch screen display or the location of an object positioned near the surface of a touch screen display. These sensors can detect the location of the object along the surface of the display, e.g. in the plane of a flat rectangular display. Examples of touch screen sensors include capacitive sensors, resistive sensors, and projected capacitive sensors. Such sensors can include transparent conductive elements that overlay the display. The elements can be combined with electronic components that use electrical signals to probe the elements in order to determine the location of an object near or in contact with the display.
Touch screen sensors are useful in electronic devices such as, for example, mobile phones, personal digital assistances (PDAs), laptop computers, and as an interface to computer systems. Recently projected capacitive touch sensor technology has been developed that allows users to interact with the touch sensor with more than one finger. The capacitance change at every individual point on, for example a sensor grid, can be measured to accurately determine the touch location or locations of one or more fingers. But projected capacitive touch sensors rely on very small changes in capacitance in the sensor. The sensitivity of projected capacitive touch sensors can be affected by stray electromagnetic radiation (e.g., electromagnetic interference, EMI) from, for example, a display device near the sensor or from electromagnetic radiation from outside the device.
Thus, there is a need for projective capacitive sensors that are highly responsive to input from a user but can resist interference from stray electric fields. There is a need for projective capacitive sensors that are very compact, transparent, and can be used in a large variety of environments. Finally, there is a need for projective capacitive sensors that are economical with regards to price, manufacturing process, and electronic real estate.